accidentally told boss

I'm 5 weeks and told a close friend at work. Apparently my boss was around the corner and overheard. This is definitely not how I planned on spilling the news. She came up to me later and asked if she heard what she thinks she heard, and I said I wasn't sure. Yes, I panicked and lied, but I don't go to the doctor for 3 more weeks. How do you think I should handle this?

Also, my boss isn't exactly cuddly either. While legally she of course can't do anything, I'm afraid she's going to make my job miserable. I was actually thinking of looking for a new job but wanted to wait while we were TTC. Her assistant announced she was pregnant with her second and she was visibly mad, and was complaining her due date messed with her vacation plans. My job requires being on my feet for the entire day and carrying heavy objects, so I will need to be on limited duty in a few months. She's not going to take this well. Any advice on how I should handle this?